President Barack Obama delivers his State of the Union address on Capitol Hill in Washington, Tuesday, Jan. 24, 2012. Listening in back are Vice President Joe Biden and House Speaker John Boehner, right. (AP Photo/Saul Loeb, Pool)

WASHINGTON (Reuters) - If Inauguration Day marked the official rollout of a tougher, bolder President Barack Obama, look for him to take it a step further on Tuesday night: his State of the Union address is expected to lay out an unabashedly liberal Democratic agenda to a U.S. Congress half controlled by conservative Republicans.

With his poll numbers up, his supporters' expectations high and Republicans still in disarray after their lackluster showing in the November election, Obama would seem to have good reason to press ahead.

But the political and fiscal realities of a divided Washington will make it difficult for him to translate the ambitious themes he articulates from the podium - a U.S. immigration overhaul, gun control, tax reform and possibly even action on climate change - into legislative form.

On top of that, Obama knows the clock is ticking.

The consensus among Washington insiders is that the Democratic president has a limited window, possibly as little as a year and a half, to push through his congressional priorities before being reduced to lame-duck status.

Obama also faces the risk of overreach, a common pitfall of second-term presidents, and his new, hard-line approach in the latest fiscal battles could alienate Republicans to the point of shutting down the cooperation he needs to gain traction for his other big-ticket plans.

Still, when Obama stands before a joint session of Congress with tens of millions watching on television, it will be his best chance to build momentum for a far-reaching agenda he laid out in his January 21 inauguration address, surprising even many traditional liberals.

Obama's aides hope that by using prime-time television on Tuesday and following that up with campaign-style trips around the country, the president can satisfy his liberal base for now and rally the American public to put pressure on Republicans.

It is a strategy that has helped him outmaneuver Republicans on fiscal matters since the election. But some political analysts are skeptical it will be enough when Republicans, who still control the House of Representatives, use their budgetary clout to block spending on Obama's new pet projects.

"Presidents have very limited ability to motivate Congress by going over their heads to the American people," said Russell Riley, an expert on presidential rhetoric at the University of Virginia.

BATTLE LINES DRAWN

With State of the Union night approaching, the ideological battle lines are already drawn.

"The inaugural address was a robust liberal vision, and this is going to be a detailed liberal plan," predicted Democratic strategist Doug Hattaway.

Once again, conservatives will not be pleased.

"If he stays on the same path as the inauguration, the president is going to come across as very in-your-face to the Republicans," Republican strategist John Feehery said.

The tone and substance of the president's annual State of the Union address are expected to fit the more forceful public persona he has struck and the tougher rhetoric he has adopted since his re-election victory against Republican Mitt Romney.

Whereas his first term was marked by complaints from some progressives that he was too accommodating to his opponents, Republicans now accuse him of kicking them while they are down.

Sounding a bit like the old Obama, the president issued a call on Thursday for humility in public life at a national prayer breakfast attended by politicians of all ideological stripes.

Just hours later, he sounded anything but humble as he stood before Democratic lawmakers gathered in Virginia and exhorted them to do what is necessary to take back the House of Representatives from Republicans in the 2014 elections. That would make life easier for him later in his second term.

Obama is likely to offer gestures of bipartisanship in the his State of the Union but with the self-assuredness of a re-elected president who will never again have to face the voters.

He is sure to stress unfinished business - dealing with a still struggling economy, a tepid job market and high deficits - coupled with his re-election campaign theme of protecting the middle class along with the country's social safety net.

He is also expected to keep up his more assertive style of demanding Republican concessions to avoid the next round of deep spending cuts, which kick in on March 1 if no deal is reached.

Obama has also made clear he plans to push for a revamp of the tax code, and he could roll out proposals to end a "carried interest" tax break used by hedge fund managers, close loopholes for the wealthy and repeal tax subsidies for big oil companies.

Following a surprisingly strong Inauguration Day pledge to tackle climate change, Obama will repeat his intention to take action, said a source familiar with the process.

But he will not lay out a detailed plan for reducing greenhouse gas emissions, saving that for later in the year - a delay that may disappoint environmentalists who hoped he would move quickly past the hesitant approach of his first term.

OBAMA LEGACY, PARTY'S FUTURE IN PLAY

Obama appears to be staking a big part of his presidential legacy on two of the most emotional issues in American politics - immigration reform and gun control - both of which will feature prominently in Tuesday's speech.

Aides say he will insist that any immigration overhaul offer a clear path to citizenship for the country's 11 million illegal immigrants - something that many Republicans oppose as "amnesty" and which is seen as a potential deal-breaker in Congress.

Obama is not ready to introduce his own bill while bipartisan efforts are under way, but his aides are confident he has enough leverage to avoid giving ground to Republicans, who were chastened by their rejection by Latino voters in the 2012 election.

The White House believes that if reform fails in Congress, voters are more likely to blame the Republicans, who would suffer the consequences in the 2014 congressional elections.

Mindful of the importance of broadening their appeal, Republicans have assigned the job of delivering the response to the State of the Union speech to Florida U.S. Senator Marco Rubio, a Cuban-American rising star in the party who is pushing a more restrictive process of legalization than Obama wants.

Obama will also seek to rally public support for gun-control proposals he laid out last month after the Newtown, Connecticut, school shooting massacre. Gun-control advocates will need the reassurance, as hopes for a swift consensus have dimmed.

Administration officials acknowledge an uphill fight in getting a ban on assault weapons, but see a better chance for agreement on requiring background checks for all gun buyers.

Obama also fired up liberals with his mention of gay rights at last month's inauguration, and they hope he will spell out details. But it was unclear how far he might go in tackling a cause popular with younger voters but not social conservatives.

Republicans believe that Obama has overstated his mandate and does not have enough political capital to juggle so many issues, especially with the economy still in the doldrums and the president facing budgetary constraints.

Examples of second-term failure abound, among them former Republican President George W. Bush's bid to overhaul Social Security, which ran afoul of public opinion and went nowhere.

Neera Tanden, president of the liberal-leaning Center for American Progress, said Obama was right to "flood the zone" with ambitious proposals and was not going too far.

Realistically, however, Obama may have no more than two years to achieve his agenda before Washington's attention turns to the 2016 presidential election race and he is sidelined as a lame duck with diminished political influence.